In certain manufacturing processes it is necessary to deposit small quantities of a liquid at specific locations, with accuracy being required both for the amount of liquid deposited and the location of the deposit. It is sometimes desired in a manufacturing process, for example, to deposit microdots of an adhesive at particular locations in the assembly of a small electronic device.
For the aforementioned purpose, dispensing syringes are used which are similar to medical hypodermic syringes and which have, at their dispensing ends, hollow needles of a desired internal diameter. When the syringes are used the manner of medical syringes with expulsion of liquid through the hand propulsion of a plunger within the syringe, it is difficult to obtain a uniformity of size in the deposited drops of liquid, particularly when the operator utilizes the syringe repeatedly for several hours on a production line and begins to show signs of fatigue. To deal with this problem, dispensers have been developed which replace the conventional syringe plunger and which expel liquid from the syringe by displacing it through the introduction of controlled charges or "shots" of pressurized gas, usually air. The dispenser is usually actuated by a foot switch, each switch contact injecting a measured microquantity of pressurized gas into the syringe and causing a measured microquantity of liquid to be expelled therefrom.
The connection between the dispenser and the syringe must be gas-tight. Conventionally, the connection comprises a flexible tube affixed at one of its ends to the dispenser and affixed at its opposite end to a tubular stopper member.
The tubular stopper member has a cylindrical portion at one end which has an outer diameter somewhat smaller than the inner diameter of the syringe at its end opposite the needle end. At a midpoint in the outer surface of the cylindrical portion there is an annular groove containing a resilient O-ring dimentioned to provide a gas-tight fit between the tubular stopper member and the inner surface of the syringe.
A flange on said tubular member terminates its cylindrical end portion and provides a limit to its insertion into the open end of the syringe; and oppositely disposed channels at opposite sides of said flange are designed to receive and hold oppositely disposed projections or "ears" at the open end of the syringe.
A suitable gas-tight fit of the tubular stopper member to the open end of the syringe requires fairly close tolerances in dimensioning of the stopper member outer diameter and fairly close tolerances in the positioning of the channels which hold the "ears" of the syringe. Syringes made by different manufacturers with the same capacity differ from each other with respect to the internal diameters of the syringe barrels and with respect to the thickness of the syringe "ears". As a result, a connector, suitable for attaching a syringe of a certain size of one manufacturer to a dispenser, becomes unsuitable when a syringe of another manufacture is used.